Since the compounds F123 and F125 may be used as substitutes for perchlorofluorocarbons (CFCs) in the field of aerosols (propellants) and in the field of refrigeration, efficient processes for their industrial production are currently being sought.
WO 95/16654 describes the placing in contact, at a temperature of 340° C., of F133a with chlorine and HF in the presence of a chromium catalyst. Although the conversion of the F133a in this reaction is high, it mainly produces 1,1,1,2-tetrafluoroethane (F134a) at this temperature. Thus, the selectivity towards F123 does not exceed 15%, which does not allow a production of this compound under industrially acceptable conditions to be envisaged.
WO 94/11327 mentions the placing in contact, at temperatures below 300° C., of F133a with chlorine and HF in the presence of a chromium catalyst. This reaction is carried out with a very large excess of chlorine and HF, and preferentially leads to the formation of F124 and F125; thus, the selectivity towards F123 remains less than 8% and the 110 series/120 series ratio is greater than 10%.
EP-A-526 908 and EP-A-346 612 propose the preparation of F123 by placing chlorine in contact with F133a, at a temperature preferably between 350 and 450° C., in the presence or absence of a catalyst, this chlorination being carried out in the absence of HF.
U.S. Pat. No. 4,145,368 proposes a process that consists in reacting chlorine with F133a, then separating the F123 from the reaction medium, and reacting the F113a resulting from this separation with a further amount of F133a, this reaction being carried out in the vapour phase and preferably between 350 and 425° C., in the presence of a catalyst such as a chromium oxide.
According to the said document, the final selectivity towards F123 does not exceed 29%.
EP-B-407 990 proposes the chlorination of F133a to F123 by thermal or catalytic activation, in the liquid phase under pressure. The selectivity towards F123 may range from 67.9 to 83.4%, the reaction pressure ranging from 50 to 127 bar.
EP-A-402 874 proposes to react chlorine with F133a between 350 and 450° C., in the absence of a catalyst and of HF. According to the said document, the production of F113a may be eliminated by means of a particular combination of temperature conditions, contact time and molar ratio of reagents.
U.S. Pat. No. 5,414,166 proposes a chlorination of F133a in the presence of hydrogen, between 250 and 500° C. and preferably between 350 and 450° C.: the selectivity towards F123 may range from 65% to 92%.
U.S. Pat. No. 5,723,700 describes a step during which F133a, HF and Cl2 react, in the presence of a fluorination catalyst, between 300 and 450° C. to give essentially F134a and traces of F123.